Approximately 35 million people worldwide are estimated to be infected with human immunodeficiency virus (HIV). Although infection rates are declining, in 2012 about 2.3 million people were newly infected and about 1.6 million people died from AIDS-related illnesses. However, viral diversity in HIV and the occurrence of escape variants provide significant challenges to development of effective HIV vaccines. Thus, there remains a need for the development of effective vaccines to treat and inhibit HIV infection worldwide.